Hitherto, there have been provided various kinds of functional deposited films which are so-called amorphous semiconductor material films. Along with the provision of such functional deposited films, there have been proposed various methods by means of a MW-PCVD process for forming them such as disclosed in the specification of U.S. Pat. No. 4,504,518.
According to such known method, it is possible to form a functional deposited film with a practically acceptable utilization efficiency of a raw material gas and also with a practically acceptable deposition rate.
However, for any of the functional deposited films obtained by means of such known MW-PCVD method, there are still unsolved problems regarding the film quality in that it has a prismatic structure and with regard to performance characteristics, particularly optical and electric characteristics upon repeated use. Because of this, they can be applied only for limited purposes, so that they are not widely usable. For instance, in the case of employing such film as a photosensitive element in electrophotographic photosensitive member or laser beam printer, although it is satisfactory in terms of dark conductivity and photoconductivity, there are problems in that the speed of response for the photoconductivity is slow and because of this, there often occur ghosts. These problems will become significant in the case of an electrophotographic photosensitive member that has a light receiving layer of large area and large layer thickness. Likewise, in the case where such film is employed as a constituent semiconductor element in solar cell, thin-film transistor, photosensor, etc., the resulting device will often exhibit a slow speed of response for photoconductivity and a lack in quick response characteristics.
The principal cause for the foregoing probelms is understood to be because it is difficult for the known MW-PCVD method to form a functional deposited film to maintain a microwave plasma discharge in a stable state for a long period of time. The microwave plasma discharge soon becomes turbulent thereby causing undesired changes particularly in the electric characteristics of the resulting film.